1. Field of the Invention
The present invention relates to a packaging method for the thermocompression bonding of a substrate and packaging components between a stage and a head by means of an interposed thermosetting adhesive.
2. Description of the Related Art
Methods in which substrates and packaging components are bonded under heat and pressure by means of interposed anisotropic conductive films (ACFs), anisotropic conductive pastes (ACPs), nonconductive films (NCFs), and other thermosetting adhesives are known as methods for mounting IC chips and other packaging components on substrates. For example, an IC chip 3 mounted on a glass substrate 1 by means of an interposed thermosetting adhesive 2 is heated and pressed between a stage 4 and a head 5 in a COG (Chip-On-Glass) assembly obtained by mounting an IC chip on the glass substrate of an LCD panel, as shown in FIG. 1. In this case, the temperature of the head 5 is commonly set to between 150 and 350xc2x0 C. In addition, the stage 4 is kept at normal temperature to prevent the thermosetting reaction of the thermosetting adhesive 2 from starting too early. An alternative is to heat the stage to a temperature below the reaction start temperature (40 to 60xc2x0 C.) in order to prevent the connection temperature from varying from one thermocompression cycle to another during the mounting step.
Thin glass substrates having low coefficients of linear expansion are commonly used in COG assemblies in order to reduce the weight of the products and to increase mounting density. For example, conventional substrates of 1.1-mm thick are being replaced with substrates of 0.7-mm thick, and conventional substrates whose coefficient of linear expansion xcex1 is about 4.8xc3x9710xe2x88x926 are being replaced with substrates of about 3.1xc3x9710xe2x88x926.
Using a substrate 1 that is thinner and has a lower xcex1-value disrupts the heat distribution of the thermosetting adhesive 2 when the IC chip 3 is mounted in the manner described above, and the substrate 1 is warped by internal stress, as shown in FIG. 2. Consequently, images become irregular, electrical resistance increases, and other problems occur when such a packaging method is applied to the glass substrate of an LCD panel.
To address these problems, attempts have been made to use low-elasticity products as thermosetting adhesives, and thus to lower the internal stress of the substrates. Using a low-elasticity thermosetting adhesive makes it possible to reduce substrate warpage but brings about the disadvantage of lower connection reliability.
It is an object of the present invention to overcome the above-described shortcomings of prior art and to prevent substrate warpage without adversely affecting connection reliability when an IC chip or other packaging component is mounted on a substrate under heat and pressure with the aid of a thermosetting adhesive.
The inventors perfected the present invention upon discovering that the stated object can be attained by adopting an arrangement in which the stage used for such thermocompression bonding is heated to a prescribed temperature.
Specifically, the present invention provides a packaging method for the thermocompression bonding of a substrate and packaging components between a stage and a head by means of an interposed thermosetting adhesive, wherein the stage temperature during thermocompression bonding is set above the temperature corresponding to the inflection point of the elastic modulus in the relationship between the elastic modulus and the temperature of the cured adhesive.
As used herein, the term xe2x80x9cstage temperaturexe2x80x9d refers to the surface temperature of the stage on the substrate side.
These and other objects, features and advantages of the present invention are described in or will become apparent from the following detailed description of the invention.